Structure for thermally assisted MRAM

ABSTRACT

A mechanism is provided for fabricating a thermally assisted magnetoresistive random access memory device. A bottom thermal barrier is formed on a bottom contact. A magnetic tunnel junction is formed on the bottom thermal barrier. The magnetic tunnel junction includes a top ferromagnetic layer formed on a tunnel barrier. The tunnel barrier is formed on a bottom ferromagnetic layer. A top thermal barrier is formed on the top ferromagnetic layer. A top contact is formed on the top thermal barrier. The top contact is reduced to a first diameter. The tunnel barrier and the bottom ferromagnetic layer each have a second diameter. The first diameter of the top contact is smaller than the second diameter.

This application claims priority to Provisional Application No.61/977,232, filed on Apr. 9, 2014, which is herein incorporated byreference in its entirety.

BACKGROUND

The present invention relates generally to magnetic memory devices, andmore specifically, to thermally assisted MRAM devices that have areduction in width/diameter above the tunnel barrier.

Magnetoresistive random access memory (MRAM) is a non-volatile computermemory (NVRAM) technology. Unlike conventional RAM chip technologies,MRAM data is not stored as electric charge or current flows, but bymagnetic storage elements. The elements are formed from twoferromagnetic plates, each of which can hold a magnetic moment,separated by a thin insulating layer. In a typical embodiment, one ofthe two plates is a reference magnet with magnetization set to aparticular polarity; the other plate's magnetization can be changed tomatch that of an external field to store memory and is termed the “freemagnet” or “free-layer”. This configuration is known as a magnetictunnel junction and is the simplest structure for a MRAM bit. A memorydevice is built from a grid of such “cells.” In some configurations ofMRAM, such as the type further discussed herein, both the reference andfree layers of the magnetic tunnel junctions can be switched using anexternal magnetic field.

SUMMARY

According to one embodiment, a method of fabricating a thermallyassisted magnetoresistive random access memory device (TAS-MRAM) isprovided. The method includes forming a bottom contact, forming a bottomthermal barrier on the bottom contact, and forming a magnetic tunneljunction on the bottom thermal barrier. The magnetic tunnel junctionincludes a top ferromagnetic layer formed on a tunnel barrier, where thetunnel barrier is formed on a bottom ferromagnetic layer. The methodincludes forming a top thermal barrier on the top ferromagnetic layer,forming a top contact on the top thermal barrier, and reducing the topcontact to a first diameter. The tunnel barrier and the bottomferromagnetic layer each have a second diameter, and the first diameterof the top contact is smaller than the second diameter.

According to one embodiment, a thermally assisted magnetoresistiverandom access memory device (TAS-MRAM) is provided. The device includesa bottom thermal barrier formed on a bottom contact, and a magnetictunnel junction formed on the bottom thermal barrier. The magnetictunnel junction includes a top ferromagnetic layer formed on a tunnelbarrier, where the tunnel barrier is formed on a bottom ferromagneticlayer. A top thermal barrier is formed on the top ferromagnetic layer,and a top contact is formed on the top thermal barrier. The top contactis reduced to a first diameter. The tunnel barrier and the bottomferromagnetic layer each have a second diameter, and the first diameterof the top contact is smaller than the second diameter.

According to one embodiment, a thermally assisted magnetoresistiverandom access memory device (TAS-MRAM) is provided. The device includesa bottom thermal barrier formed on a bottom contact, a bottomferromagnetic layer formed on the bottom thermal barrier, a left tunnelbarrier and a right tunnel barrier both formed on the bottomferromagnetic layer, and a left top ferromagnetic layer formed on theleft tunnel barrier. The device also includes a right top ferromagneticlayer formed on the right tunnel barrier, a left top thermal barrierformed on the left top ferromagnetic layer, a right top thermal barrierformed on the right top ferromagnetic layer, a left top contact formedon the left top ferromagnetic layer, and a right top contact formed onthe right top ferromagnetic layer.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1A illustrates a thermally-assisted magnetoresistive random accessmemory (TAS-MRAM) device.

FIG. 1B illustrates a thermally-assisted magnetoresistive random accessmemory (TAS-MRAM) device.

FIG. 1C illustrates a thermally-assisted magnetoresistive random accessmemory (TAS-MRAM) device according to an embodiment.

FIGS. 2A through 2E illustrate a fabrication process to form athermally-assisted magnetoresistive random access memory (TAS-MRAM)device according to an embodiment, which includes:

FIG. 2A illustrating layers of the MRAM device;

FIG. 2B illustrating etching the top contact;

FIG. 2C illustrating depositing conformal encapsulating layers;

FIG. 2D illustrating directional etching to remove the conformalencapsulating from the horizontal surfaces but not vertical surfaces;and

FIG. 2E illustrating completion of the MRAM device.

FIGS. 3A, 3B, and 3C illustrate a fabrication process to form athermally-assisted magnetoresistive random access memory deviceaccording to an embodiment, which includes:

FIG. 3A illustrating etching the top contact, top thermal barrier, andthe top ferromagnetic layer;

FIG. 3B illustrating directional etching to remove the conformalencapsulating from the horizontal surfaces but not the verticalsurfaces; and

FIG. 3C illustrating completion of the MRAM device.

FIG. 4A illustrates a thermally-assisted magnetoresistive random accessmemory device according to an embodiment.

FIG. 4B illustrates a thermally-assisted magnetoresistive random accessmemory device according to an embodiment.

FIG. 4C illustrates a thermally-assisted magnetoresistive random accessmemory device according to an embodiment.

FIG. 5 illustrates a thermally-assisted magnetoresistive random accessmemory device according to an embodiment.

FIG. 6 illustrates a method of fabricating/forming a thermally assistedmagnetoresistive random access memory device according to an embodiment.

DETAILED DESCRIPTION

Embodiments relate to thermally-assisted magnetoresistive random accessmemory (MRAM) devices that use a self-reference read-out scheme. Whenwriting, current (i.e., heating current) flows though the MRAM device toheat it up above a blocking temperature, and at the same time currentflows through a neighboring (field) wire to generate a magnetic fieldthat sets the desired orientation of the storage layer. Smaller devices(e.g., in width and/or diameter) require less current to heat the MRAMdevice but a larger (magnitude) magnetic field and therefore largercurrent to generate the magnetic field.

The MRAM device must have high enough of a resistance to be compatiblewith the select transistor, which limits how large the storage layer canbe made. The select transistor is used as a switch to turn on and offthe writing (heating) current for the MRAM device.

The MRAM device is usually manufactured to have the same diameter forthe various layers. However, by stopping the device etch close to theactive tunnel barrier, the storage layer can be kept large, while thethermal volume is reduced and the device resistance increased accordingto embodiments.

Embodiments disclose a fabrication process in which the etch process isinterrupted to define an MRAM device with two diameters: one largediameter for the storage layer, one smaller diameter (of various layersabove the tunnel barrier) for the current flow. In one implementation,the first etch stops on the tunnel barrier, then a conformalencapsulation layer is applied, and finally a directional etch isapplied to complete the etching.

Further details regarding writing to the TAS-MRAM device include heatingthe magnetic tunnel junction (MTJ) stack to a write temperature(T_(write)) higher than the maximum storage temperature (T_(store)) inorder to write to the device. The (MTJ of the) device consists of astorage magnetic layer, and a sense magnetic layer, separated by anon-magnetic tunnel barrier. The electrical resistance of this stackdepends on the relative magnetic orientation of the parts of the storageand sense layers that interface with the tunnel barrier; this effect iscaused by the phenomenon of tunneling magnetoresistance (TMR). Intypical devices, an antiferromagnetic layer pins the storage layer attemperatures T_(MRAM)<T_(store), where T_(MRAM) is defined as thetemperature of the magnetic tunnel junction (and antiferromagneticlayers). The sense magnetic layer is free to switch back and forth by anapplied magnetic field. If the magnetic orientation of the sense layeris parallel to the magnetic orientation of the storage layer, then theMTJ stack will have low resistance; if the sense layer is anti-parallelto the storage layer, the stack will have high resistance. The device isread out by toggling the sense layer in both directions by an appliedmagnetic field of two known directions, and determining the direction ofthe storage layer based on the sign of the resistance change.

The MRAM device is written when the temperature of the MRAM device isT_(MRAM)≧T_(write); in this case, the pinning by the antiferromagnet isreduced and the storage layer can be re-oriented into a new direction byan applied magnetic field of known direction. One direction is chosen asa logical “1” state, while the other is chosen as a logical “0” state.

The storage layer may consist of a single magnetic layer, or a syntheticantiferromagnetic layer; each of these magnetic layers may in turnconsist of several distinct, alloy, or compound materials and materiallayers.

FIGS. 1A, 1B, and 1C (generally referred to as FIG. 1) illustrate acomparison of structures for thermally-assisted magnetoresistive randomaccess memory (TAS-MRAM) devices according to an embodiment. FIG. 1depicts cross-sectional views of the MRAM devices.

FIG. 1A illustrates a narrow device 10. FIG. 1B illustrates a widedevice 20. FIG. 1C illustrates the stop above barrier device 30according to an embodiment. In each case, each of the MRAM devices hasidentical layers except their diameters (i.e., widths) are different.Each MRAM device has a top contact 5 which may be a metal contact (orconductor), a ferromagnetic sense layer 7 (also referred to as the freelayer), an active tunnel barrier 9 (also referred to as a heatingbarrier), a ferromagnetic storage layer 11, and a bottom contact 13which may be a metal contact (or conductor). The difference between thestructures is the diameter (d) of the MRAM device in FIGS. 1A, 1B, and1C.

To simplify, it is assumed that the thermal loss is proportional to thecross-sectional area of the pillar on both sides (above and below) ofthe tunnel barrier 9. Voltage is fixed, and the current is selected togenerate enough thermal power to balance the loss. The current needed isproportional to the cross-sectional areas of contact 5 and 13, while theresistance is defined by the black (active) tunnel barrier 9.

The narrow device 10 has a thermal loss area designated as Area_a. Thewide device 20 has a thermal loss area Area_b=4·(Area_a). The (etching)stop above barrier device 30 has a thermal loss areaArea_c=2.5·(Area_a).

The advantage of the wide device 20 and (stop over barrier) device 30over the narrow device 10 is that the storage and free layers 11 and 7are twice as large and require about half the magnitude of magneticfield to write and read. The current of the wide device 20 is definedby: I_b=4*I_a (R is 4× (i.e., 4 times) smaller than A, the transistorwidth 4× larger, and same RA), where R is resistance, A is area of theparticular device, and I_a is the current of the device 10 in FIG. 1A.

The current of the stop over barrier device 30 is defined by:I_c=2.5*I_a (R is 2.5× smaller than A, the select transistor width 2.5×larger, RA=4/2.5=1.6 times larger). Note that the select transistor isnot shown but the width of the select transistor is based on the amountof heating current needed, which is I_c in FIG. 1C.

If the larger size of wide device 20 is necessary to reduce themagnitude of the magnetic fields, trimming the top contact 5 reduces therequired thermal power (i.e., I_c). Comparing the stop over barrierdevice 30 to the wide device 20, the device resistance is larger by4/2.5=1.6, and the circuit size of device 30 can be reduced by 1.6×.Also, RA is also larger by 1.6×. That is, FIG. 1C requires less writing(heating) current than FIG. 1B, and less magnitude of the magnetic field(i.e., field current) than FIG. 1A. In addition, the barrier is morerobust because of the larger RA. Note than other examples of the stopover barrier device are provided herein.

FIGS. 2A through 2E (generally referred to as FIG. 2) illustrate afabrication process for a thermally-assisted magnetoresistive randomaccess memory (TAS-MRAM) device 200 according to an embodiment. Variouscross-sectional views are shown for making the MRAM device 200. FIG. 2illustrates one example of a stop on or above the barrier device. Oneskilled in the art understands that other embodiments discussed hereincan be made according to the example below.

FIG. 2A illustrates that a bottom electrode 19 is formed and the bottomcontact 13 is deposited on top of the bottom electrode 19. The bottomelectrode 19 and the bottom contact 13 may both be a metal or anysuitable conductor. A thermal barrier 17 is deposited on top of thebottom contact 13. The ferromagnetic storage layer 11 is deposited onthe bottom thermal barrier 17. The (active) tunnel barrier 9 (which hasTMR necessary to read out the MRAM device 200) is deposited on theferromagnetic storage layer 11. The ferromagnetic sense layer 7 isdeposited on the tunnel barrier 9. A top thermal barrier 15 is depositedon the ferromagnetic sense layer 7. The top contact 5 is deposited onthe top thermal barrier 15.

Example materials of the thermal barriers 15 and 17 include BiTe,GeSbTe, and SiCOH. When electrical (writing) current is applied to heatthe tunnel barrier 9, the thermal barriers 15 and 17 help to maintainheat in between thermal barriers 15 and 17, thus preventing heat loss.The material of the tunnel barrier 9 may include MgO.

Example ferromagnetic materials of the ferromagnetic sense layer 7 andferromagnetic storage layer 11 include Co, Fe, and/or Ni, along with anyalloy of these materials.

A photoresist layer 20 is deposited on the top contact 5. Thephotoresist layer 20 is patterned in the desired width (diameter) forthe shaping the top contact 5 (and top thermal barrier 15) below. (Notethat the diameter of the photoresist layer 20 is utilized for etchingother layers as discussed in other embodiments). FIG. 2B illustratesetching the top contact 5 and the top thermal barrier 15 into thecorresponding/matching diameter of the photoresist 20 above. In thisimplementation the depth of etching is through the top thermal barrier15. This implementation shows that both the top contact 5 and the topthermal barrier 15 have been reduced in diameter.

One implementation may only reduce the diameter of the top contact 5 tothe narrow width of the photoresist 20, so that the etching stops at thetop thermal barrier 15 but not through the thermal barrier 15 (as shownin FIG. 4B). Another implementation may additionally etch through theferromagnetic sense layer 7, along with the top contact 5 and the topthermal barrier 15, such that the ferromagnetic sense layer 7 also hasthe narrow width of the photoresist 20 (as shown in FIG. 3). Etching isto stop above and/or on the tunnel barrier 9, without etching the tunnelbarrier 9 to the narrow width of the photoresist layer 20.

FIG. 2C illustrates depositing conformal encapsulating layers 22 (e.g.,via spin-on deposition) on all surfaces. FIG. 2D illustrates usingdirectional etching to remove the conformal encapsulating layers 22 fromthe horizontal surfaces. The conformal encapsulating layers 22 remainvertically around the perimeter of the photoresist 20, top contact 5,and top thermal barrier 15. The conformal encapsulating layers 22 areconfigured not to conduct electricity. Examples of the conformalencapsulating layers 22 include insulators, such as silicon dioxide,silicon nitride, etc.

FIG. 2E illustrates completing the MRAM device 200 by etching down tothe electrode 19. As can be seen, the ferromagnetic sense layer 7,tunnel barrier 9, ferromagnetic storage layer 11, bottom thermal barrier17, and bottom contact layer 13 are etched to a width/diameter thatcorrespond to (i.e., matches) the combined width of the (left and right)conformal encapsulating layers 22 plus the photoresist 20. The conformalencapsulating layers 22 were added so that the top contact 5 plusconformal encapsulating layers 22 on the left and right have a matchingdiameter (D2) as the ferromagnetic sense layer 7, tunnel barrier 9,ferromagnetic storage layer 11, bottom thermal barrier 17, and bottomcontact layer 13.

For example, the diameter of the top contact 5, the top thermal contact15, and photoresist 20 are each D1. The example range of diameter D1 maybe 25-100 nanometers (nm). Particularly, the diameter D1 may be 25-50 nmwhich maintains a lower heating current but keeps the magnitude of themagnetic field manageable 50-200 Oersted given the narrowed width of thetop contact 5.

The layers (the ferromagnetic sense layer 7, tunnel barrier 9,ferromagnetic storage layer 11, bottom thermal barrier 17, and bottomcontact layer 13) below the top thermal contact 15 each have a diameterD2. The diameter D2 may be 200-500 nm. Although ranges are provided fordiameters D1 and D2, it is noted that the relationship of the smallerdiameter D1 to larger diameter D2 is intended such that diameter D1 isalways smaller than diameter D2 by 20 nm or more (particularly 50 nmsmaller). In one embodiment, the smaller diameter D1 is configured to behalf the diameter D2 for any diameter selected within the range ofdiameter D1 or diameter D2.

FIGS. 3A, 3B, and 3C (generally referred to as FIG. 3) illustrate afabrication process for a thermally-assisted magnetoresistive randomaccess memory (TAS-MRAM) device 300 according to an embodiment. Variouscross-sectional views are shown for making the MRAM device 300. FIG. 3illustrates one example of a stop on or above the barrier device thatetches through the top ferromagnetic layer, which in this case is theferromagnetic sense layer 7. In one embodiment, the magnetic tunneljunction (MTJ) may include the ferromagnetic storage layer 11 depositedon top of the tunnel barrier 9, and the tunnel barrier 9 deposited ontop of the ferromagnetic sense layer 7. In this embodiment, the etchingwould extend down through the ferromagnetic storage layer 11 which isnow the top ferromagnetic layer in the magnetic tunnel junction.

Referring back to FIG. 3, FIG. 3 includes the same materials (layers)that have been discussed above in FIG. 2, except that instead of onlyetching through the top contact 5 and top thermal barrier 15 in FIG. 2,FIG. 3 etches the smaller diameter D1 through the top contact 5, topthermal barrier 15, and the top ferromagnetic sense layer 7. For thesake of conciseness, some processes in the fabrication processpreviously discussed in FIG. 2 are not repeated in FIG. 3 but apply byanalogy.

As previously shown in FIG. 2A (but not repeated in FIG. 3), the bottomelectrode 19 is formed and the bottom contact 13 is deposited on top ofthe bottom electrode 19. The bottom electrode 19 and the bottom contact13 may both be a metal or any suitable conductor. The thermal barrier 17is deposited on top of the bottom contact 13. The ferromagnetic storagelayer 11 is deposited on the bottom thermal barrier 17. The (active)tunnel barrier 9 (which has TMR necessary to read out the MRAM device200) is deposited on the ferromagnetic storage layer 11. Theferromagnetic sense layer 7 is deposited on the tunnel barrier 9. Thetop thermal barrier 15 is deposited on the ferromagnetic sense layer 7,and the top contact 5 is deposited on the top thermal barrier 15. Thephotoresist layer 20 is deposited on the top contact 5. The photoresistlayer 20 is patterned in the desired width (diameter) for the shapingthe top contact 5, the thermal barrier 15, and the ferromagnetic senselayer 7 below (but not through the tunnel barrier 9). After the processshown in FIG. 2A, the fabrication flows to FIG. 3A.

FIG. 3A illustrates etching the top contact 5, the top thermal barrier15, and the ferromagnetic sense layer 7 into the matching diameter D1 ofthe photoresist 20 above. FIG. 3A shows that the top contact 5, the topthermal barrier 15, and the ferromagnetic sense layer 7 (shown asnarrowed portion 305) have been narrowed to diameter D1.

As previously shown in FIG. 2C (but not repeated in FIG. 3), conformalencapsulating layers 22 (e.g., via spin-on deposition) is deposited onall surfaces. In FIG. 3, the conformal encapsulating layers 22 islikewise deposited on the tunnel barrier 9 (not shown in FIG. 3B), onthe top of the photoresist 20 (not shown in FIG. 3B), and on the leftand right sides of the narrowed portion 305. After the process shown inFIG. 2C, FIG. 3B illustrates using directional etching to remove theconformal encapsulating layers 22 from the horizontal surfaces. Theconformal encapsulating layers 22 remain on the perimeter of thephotoresist 20, top contact 5, top thermal barrier 15, and ferromagneticsense layer 7. The conformal encapsulating layers 22 are configured notto conduct electricity. Examples of the conformal encapsulating layers22 include oxides, such as silicon dioxide, etc.

FIG. 3C illustrates completing the MRAM device 300 by etching theremaining layers down to the electrode 19 (but not through). As can beseen, the tunnel barrier 9, ferromagnetic storage layer 11, bottomthermal barrier 17, and bottom contact layer 13 are etched to a widththat matches (i.e., is the same as) the combined width of the (left andright) conformal encapsulating layers 22 plus the photoresist 20. Theconformal encapsulating layers 22 were added so that the narrowed topcontact 5, narrowed thermal barrier 15, the ferromagnetic sense layer 7plus conformal encapsulating layers 22 on the left and right (together)have a matching diameter D2 as the tunnel barrier 9, ferromagneticstorage layer 11, bottom thermal barrier 17, and bottom contact layer13.

For example, the diameter of the top contact 5, the top thermal barrier15, photoresist 20, and ferromagnetic sense layer 7 are each D1. Theexample range of diameter D1 may be 25-100 nanometers (nm).Particularly, the diameter D1 may be 25-50 nm which maintains a lowerheating current but keeps the magnetic field manageable 50-200 Oerstedgiven the narrowed width of the top contact 5, the ferromagnetic senselayer 7.

The layers (tunnel barrier 9, ferromagnetic storage layer 11, bottomthermal barrier 17, and bottom contact layer 13) below the ferromagneticsense layer 7 each have the diameter D2. The diameter D2 may be 200-500nm. Although ranges are provided for diameters D1 and D2, it is notedthat the relationship of the smaller diameter D1 to larger diameter D2is intended such that diameter D1 is always smaller than diameter D2 by20 nm or more (particularly 50 nm smaller). In one embodiment, thesmaller diameter D1 is configured to be half the diameter D2 for anydiameter selected within the range of diameter D1 or diameter D2.

Now turning to additional embodiments illustrating etching to stop on orabove the tunnel barrier 9, FIGS. 4A, 4B, and 4C provide additionalexamples according to embodiments. Although understood to beincorporated, FIGS. 4A, 4B, and 4C omit the additional layers discussedin FIGS. 2 and 3.

FIG. 4A illustrates etching down through only part of the ferromagneticsense layer 7 in order to narrow only the upper part but not entirelythrough the ferromagnetic sense layer 7. This etching results in theferromagnetic sense layer 7 having an upper part 405 with height H1 anda bottom part 410 with height H2. The heights H1 and H2 may be equal (ornearly equal), the height H1 may be more than height H2, and/or theheight H2 may be more than the height H1. Examples of the height H1 mayinclude 0.1-2 nm. Examples of the height H2 may include 0.1-2 nm.Although overlapping or nearly overlapping dimensions may be given, theheights H1 and H2 are utilized to maintain one of the heightrelationships discussed above. Accordingly, the upper part 405 of theferromagnetic sense layer 7 has the narrow diameter D1 while the bottompart 410 has the larger diameter D2.

FIG. 4B illustrates etching down only through the top contact 15 but notetching through the thermal barrier 15.

FIG. 4C illustrates etching down through only part of the top contact 5in order to narrow only the upper part but not entirely through the topcontact 5. This etching results in the top contact 5 having an upperpart 415 with height H3 and a bottom part 420 with height H4. Theheights H3 and H4 may be equal (or nearly equal), the height H3 may bemore than height H4, and/or the height H3 may be more than the heightH4. Examples of the height H3 may include 1-200 nm. Examples of theheight H4 may include 0.1-20 nm. Although overlapping or nearlyoverlapping dimensions may be given, the heights H3 and H4 are utilizedto maintain one of the height relationships discussed above.Accordingly, the upper part 415 of the top contact 5 has the narrowdiameter D1 while the bottom part 420 has the larger diameter D2.

Now turning to FIG. 5, another example of a cross-sectional view of athermally assisted magnetoresistive random access memory device(TAS-MRAM) 500 is provided according to an embodiment. The MRAM device500 operates as one single MRAM device with series junctions. The MRAMdevice 500 includes the materials (layers) discussed in FIG. 2, andreference can be made to FIG. 2 for example materials. However, in FIG.5, left and right upper electrodes 505A and 505B are added.

The bottom electrode 19 is formed and the bottom contact 13 is depositedon top of the bottom electrode 19. The thermal barrier 17 is depositedon top of the bottom contact 13. The ferromagnetic storage layer 11 isdeposited on the bottom thermal barrier 17. The (active) tunnel barrier9 (which has TMR necessary to read out the MRAM device 500) is depositedon the ferromagnetic storage layer 11 and patterned to form left andright tunnel barriers 9A and 9B. In one case, the left and right tunnelbarriers 9A and 9B are configured to (partially) touch one another onthe ferromagnetic storage layer 11. In another case, the left and righttunnel barrier 9A and 9B are formed to be separate from one another soas not to touch each other on the ferromagnetic storage layer 11. Theferromagnetic sense layer 7 is deposited on the tunnel barrier 9 andetched to have left and right ferromagnetic sense layers 7A and 7B. Thetop thermal barrier 15 is deposited on the ferromagnetic sense layer 7and patterned to have top thermal barriers 15A and 15B. The top contact5 is deposited on the top thermal barrier 15 and patterned to have leftand right top contacts 5A and 5B.

Additionally, the top electrodes 505A and 505B are deposited on the topcontact 5 and patterned to have left and right parts. A field wire 515provides the magnetic field when an electrical current is appliedthrough the field wire 515. This same field wire 515 may be utilized togenerate the magnetic field in FIGS. 1-6 discussed herein.

The MRAM device 500 shows that directional etching is applied to reducethe diameter of layers in the device. Particularly, etching in thecenter narrows and forms the two contacts 5A and 5B, the thermalbarriers 15A and 15B, ferromagnetic sense layers 7A and 7B, and tunnelbarriers 9A and 9B.

During writing or reading operations, current flows from electrode 505Athrough 5A, 15A, 7A, 9A to layers 11, 17, 13, 19. The current flowacross layers 11, 17, 13, 19 and then back up through 9B, 7B, 15B, 5B toelectrode 505B. For writing, a larger current is used to heat up thedevice to T_(write). The storage layer is oriented in a desireddirection while the device is allowed to cool down below T_(store). Thedata is stored in the magnetic orientation of the storage layer. Whenreading, a smaller current is used to probe the resistance of the devicewhile staying below T_(store). The stored data is revealed by the signof the resistance change for different orientations of the sense layer.

For illustration purposes, various deposition techniques are discussedbelow and can be utilized in embodiments, as understood by one ofordinary skill in the art. Thin film deposition is the act of applying athin film to a surface which is any technique for depositing a thin filmof material onto a substrate or onto previously deposited layers. Thinis a relative term, but most deposition techniques control layerthickness within a few tens of nanometers. Molecular beam epitaxy allowsa single layer of atoms to be deposited at a time. Deposition techniquesfall into two broad categories, depending on whether the process isprimarily chemical or physical. Chemical vapor deposition utilizes afluid precursor that undergoes a chemical change at a solid surface,leaving a solid layer. Chemical deposition is further categorized by thephase of the precursor and examples of chemical deposition include, butare not limited to: plating; chemical solution deposition (CSD) orchemical bath deposition (CBD); spin coating or spin casting; chemicalvapor deposition (CVD); plasma enhanced CVD (PECVD); atomic layerdeposition (ALD); and so forth.

Physical vapor deposition (PVD) uses mechanical, electromechanical, orthermodynamic means to produce a thin film of solid. Examples ofphysical deposition include but are not limited to: a thermal evaporator(i.e., molecular beam epitaxy); an electron beam evaporator; sputtering;pulsed laser deposition; cathodic arc physical vapor deposition(arc-PVD); electrohydrodynamic deposition (electrospray deposition);reactive PVD; and so forth.

FIG. 6 illustrates a method 600 of fabricating/forming a thermallyassisted magnetoresistive random access memory device (TAS-MRAM)according to an embodiment. Reference can be made to FIGS. 1, 2, 3, and4 discussed herein.

At block 605, the bottom contact 13 is formed on the electrode 19. Thebottom thermal barrier 17 is formed on the bottom contact 13 at block610.

At block 615, a magnetic tunnel junction is formed on the bottom thermalbarrier 17, in which the magnetic tunnel junction includes the topferromagnetic layer 7 formed on the tunnel barrier 9 and the tunnelbarrier 9 formed on bottom ferromagnetic layer 11.

At block 620, the top thermal barrier 15 is formed on the topferromagnetic layer 7. At block 625, the top contact 5 is formed on thetop thermal barrier 15.

At block 630, the diameter of the top contact 5 is reduced (via etching)to a first diameter (e.g., narrow diameter D1). At block 635, the tunnelbarrier 9 and the bottom ferromagnetic layer 11 each have a seconddiameter D2 (e.g., reduced in size by etching), and the first diameterD1 of the top contact 5 is smaller than the second diameter D2. Examplesof the first diameter D1 and the second diameter D2 are shown in FIGS.2, 3, and 4.

The encapsulating conformal layer 22 is formed on the horizontal sides(i.e., perimeter) around the top contact 5, such that a combineddiameter of the (left and right sides in cross-sectional view)encapsulating conformal layer 22 and the top contact 5 approximatelymatches (and/or is) the second diameter D2.

The top thermal barrier 15 is reduced (via etching) to the firstdiameter D1. The encapsulating conformal layer 22 is formed onhorizontal sides around the top thermal barrier 15, such that a combineddiameter of the encapsulating conformal layer 22 and the top thermalbarrier 15 approximately matches (and/or is) the second diameter D2.

The top ferromagnetic layer 7 is reduced to the first diameter D1 asshow in FIG. 3. The encapsulating conformal layer 22 is formed onhorizontal sides around the top ferromagnetic layer 7, such that acombined diameter of the encapsulating conformal layer 22 and the topferromagnetic layer 7 approximately matches (and/or is) the seconddiameter D2.

The top ferromagnetic layer 7 has the first diameter D1 that is smallerthan the second diameter D2 of the tunnel barrier 9 and the bottomferromagnetic layer 11.

In one implementation, the top ferromagnetic layer may be aferromagnetic sense layer and the bottom ferromagnetic layer may be aferromagnetic storage layer, which has been generally described herein.However, examples are not meant to be limited to this implementation,and the ferromagnetic layers may be reversed.

For example, another implementation, the top ferromagnetic layer may bea ferromagnetic storage layer while the bottom ferromagnetic layer maybe the ferromagnetic sense layer.

Reducing the top contact 5 to the first diameter D1 may includesreducing the upper part 415 of the top contact 5 to the first diameterD1 while reducing the bottom part 420 of the top contact 5 to the seconddiameter D2, as shown in FIG. 4C.

The formation of the MRAM device may include reducing an upper part 405of the top ferromagnetic layer 7 to the first diameter D1 while reducingthe bottom part 410 of the top ferromagnetic layer 7 to the seconddiameter D2, as shown in FIG. 4A.

In FIG. 4, note that the encapsulating conformal layer 22 is not shownon the horizontal sides (i.e., perimeter) around the respective layersthat have the narrow diameter D1, so as not to obscure details in FIG.4. However, as discussed herein, the encapsulating conformal layer 22 ismeant and understood to be present around each layer (such asparts/layers 5, 15, 405 and 415) when shown or designated to have thenarrow diameter D1 in FIG. 4.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. A method of fabricating a thermally assistedmagnetoresistive random access memory device (TAS-MRAM), the methodcomprising: forming a bottom contact; forming a bottom thermal barrieron the bottom contact; forming a magnetic tunnel junction on the bottomthermal barrier, the magnetic tunnel junction including a topferromagnetic layer formed on a tunnel barrier, the tunnel barrier beingformed on a bottom ferromagnetic layer; forming a top thermal barrier onthe top ferromagnetic layer; forming a top contact on the top thermalbarrier; and reducing the top contact to a first diameter; wherein thetunnel barrier and the bottom ferromagnetic layer each have a seconddiameter, the first diameter of the top contact being smaller than thesecond diameter; the method further comprising reducing an upper part ofthe top ferromagnetic layer to the first diameter while reducing abottom part of the top ferromagnetic layer to the second diameter. 2.The method of claim 1, further comprising forming an encapsulatingconformal layer on horizontal sides around the top contact, such that acombined diameter of the encapsulating conformal layer and the topcontact approximately matches the second diameter.
 3. The method ofclaim 1, further comprising reducing the top thermal barrier to thefirst diameter; and forming the encapsulating conformal layer onhorizontal sides around the top thermal barrier, such that a combineddiameter of the encapsulating conformal layer and the top thermalbarrier approximately matches the second diameter.
 4. The method ofclaim 1, further comprising reducing the top ferromagnetic layer to thefirst diameter; and forming the encapsulating conformal layer onhorizontal sides around the top ferromagnetic layer, such that acombined diameter of the encapsulating conformal layer and the topferromagnetic layer approximately matches the second diameter.
 5. Themethod of claim 4, wherein the top ferromagnetic layer has the firstdiameter that is smaller than the second diameter of the tunnel barrierand the bottom ferromagnetic layer.
 6. The method of claim 5, whereinthe top ferromagnetic layer is a ferromagnetic sense layer; and whereinthe bottom ferromagnetic layer is a ferromagnetic storage layer.
 7. Themethod of claim 5, wherein the top ferromagnetic layer is aferromagnetic storage layer; and wherein the bottom ferromagnetic layeris a ferromagnetic sense layer.
 8. The method of claim 1, whereinreducing the top contact to the first diameter includes reducing anupper part of the top contact to the first diameter while reducing abottom part of the top contact to the second diameter.
 9. A thermallyassisted magnetoresistive random access memory device (TAS-MRAM), thedevice comprising: a bottom thermal barrier formed on a bottom contact;a magnetic tunnel junction formed on the bottom thermal barrier, themagnetic tunnel junction including a top ferromagnetic layer formed on atunnel barrier, the tunnel barrier being formed on a bottomferromagnetic layer; a top thermal barrier formed on the topferromagnetic layer; and a top contact formed on the top thermalbarrier; wherein the top contact is reduced to a first diameter; andwherein the tunnel barrier and the bottom ferromagnetic layer each havea second diameter, the first diameter of the top contact being smallerthan the second diameter; wherein an upper part of the top ferromagneticlayer is reduced to the first diameter while reducing a bottom part ofthe top ferromagnetic layer to the second diameter.
 10. The device ofclaim 9, further comprising an encapsulating conformal layer formed onhorizontal sides around the top contact, such that a combined diameterof the encapsulating conformal layer and the top contact approximatelymatches the second diameter.
 11. The device of claim 9, wherein the topthermal barrier is reduced to the first diameter; and forming theencapsulating conformal layer on horizontal sides around the top thermalbarrier, such that a combined diameter of the encapsulating conformallayer and the top thermal barrier approximately matches the seconddiameter.
 12. The device of claim 9, wherein the top ferromagnetic layeris reduced to the first diameter; and wherein the encapsulatingconformal layer is formed on horizontal sides around the topferromagnetic layer, such that a combined diameter of the encapsulatingconformal layer and the top ferromagnetic layer approximately matchesthe second diameter.
 13. The device of claim 12, wherein the topferromagnetic layer has the first diameter that is smaller than thesecond diameter of the tunnel barrier and the bottom ferromagneticlayer.
 14. The device of claim 13, wherein the top ferromagnetic layeris a ferromagnetic sense layer; and wherein the bottom ferromagneticlayer is a ferromagnetic storage layer.
 15. The device of claim 13,wherein the top ferromagnetic layer is a ferromagnetic storage layer;and wherein the bottom ferromagnetic layer is a ferromagnetic senselayer.
 16. The device of claim 9, wherein reducing the top contact tothe first diameter includes reducing an upper part of the top contact tothe first diameter while reducing a bottom part of the top contact tothe second diameter.